1. Field of Invention
The invention relates generally to an apparatus for supporting a substrate in a semiconductor processing chamber.
2. Background of the Invention
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes. One fabrication process frequently used is chemical vapor deposition (CVD).
Chemical vapor deposition is generally employed to deposit a thin film on a substrate, such as a semiconductor wafer. Chemical vapor deposition is generally accomplished by introducing a precursor gas in to a vacuum chamber. The precursor gas is typically directed through a showerhead situated near the top of the chamber. The precursor gas reacts to form a layer of material on a surface of the substrate that is positioned on a heated substrate support. Purge gas is routed through holes in the support to the edge of the substrate to prevent deposition at the substrate""s edge that may cause the substrate to adhere to the support or flake off during processing. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
One material frequently formed on substrates using a chemical vapor deposition process is tungsten. A precursor gas that may be used to form tungsten generally includes tungsten hexafluoride (WF6) and silane. As the silane and tungsten hexafluoride mix, some xe2x80x9cstrayxe2x80x9d tungsten (i.e., tungsten that does not deposit on the substrate) deposits on the showerhead and other chamber components. The stray tungsten film builds on the showerhead and may become a source of contamination in the chamber. Eventually, the stray tungsten may clog the holes in the showerhead that facilitate the passage of the precursor gas therethrough necessitating the showerhead be removed and cleaned or replaced.
To extend the interval in time between the routine maintenance of the showerhead, fluorine based chemistries are generally used to clean (i.e., etch away) the stray tungsten film. However, the use of fluorine, while advantageous for removing tungsten, reacts to form a layer of aluminum fluoride on the heated support that is commonly made of aluminum. The aluminum fluoride layer has a generally rough surface topography. The rough surface creates a leak path that impairs the vacuum used to chuck or hold the substrate to the heated support. Additionally, the aluminum fluoride layer is a potential source of particulate contamination.
Substrate supports fabricated from ceramic materials provide an improvement over aluminum supports due to ceramic""s resistance to fluorine. However, ceramic support plates are difficult and expensive to fabricate. For example, the holes in support plate used to provide purge gas to the perimeter of the support are typically drilled from the perimeter of the support to a depth generally equal to the radius of the support. Drilling such a deep hole in ceramic is difficult. The tools used to make these holes are frequently broken during the fabrication (e.g., drilling) process. Broken tools disposed within the support must be removed or the support must be scrapped. These fabrication difficulties result in costly supports and an undesirable high scrap rate.
Therefore, there is a need in the art for an improved heated support for chemical vapor deposition processes.
One aspect of the present invention generally provides a support assembly for supporting a workpiece. In one embodiment, the support assembly includes a support plate supported by a second plate. The support plate has a first side and a second side. The second side of the support has a recess formed therein. The second plate includes a boss extending from the second plate which mates with the recess of the support plate.
In another embodiment, a support assembly includes a support plate and a second plate disposed proximate the support plate. The support plate has a first side and a second side. The second side of the support plate includes a plurality of sleeves protruding therefrom. The second plate has a plurality of holes disposed therein. Each sleeve of the support plate extends at least partially into a respective one of the holes.
In another embodiment, a support assembly includes a ceramic support plate, a second plate and a purge ring. The support plate is supported by the second plate. The ceramic support plate includes a flange that extends from the plate""s perimeter. The purge ring is disposed on the flange and defines a channel between the ring and the support plate. The channel is adapted to flow a fluid adjacent a perimeter of the workpiece.